linux-hardening - Re: [PATCH][next] UAPI: ndctl / acpi: intel: Avoid multiple -Wflex-array-member-not-at-end warnings

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Message-ID: <202505061135.C76B6CA9F@keescook>
Date: Tue, 6 May 2025 11:37:28 -0700
From: Kees Cook <kees@...nel.org>
To: Alison Schofield <alison.schofield@...el.com>
Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>, justinstitt@...gle.com,
	Dan Williams <dan.j.williams@...el.com>,
	Vishal Verma <vishal.l.verma@...el.com>,
	Dave Jiang <dave.jiang@...el.com>, Ira Weiny <ira.weiny@...el.com>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Len Brown <lenb@...nel.org>, nvdimm@...ts.linux.dev,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] UAPI: ndctl / acpi: intel: Avoid multiple
 -Wflex-array-member-not-at-end warnings

On Mon, Apr 07, 2025 at 11:11:08AM -0700, Kees Cook wrote:
> On Thu, Feb 13, 2025 at 02:25:27PM -0800, Alison Schofield wrote:
> > On Thu, Feb 13, 2025 at 03:29:12PM +1030, Gustavo A. R. Silva wrote:
> > > -Wflex-array-member-not-at-end was introduced in GCC-14, and we are
> > > getting ready to enable it, globally.
> > > 
> > > So, in order to avoid ending up with flexible-array members in the
> > > middle of other structs, we use the `__struct_group()` helper to
> > > separate the flexible array from the rest of the members in the
> > > flexible structure. We then use the newly created tagged `struct
> > > nd_cmd_pkg_hdr` to replace the type of the objects causing trouble
> > > (`pkg`) in multiple structs.
> > > 
> > > So, with these changes, fix the following warnings:
> > > 
> > > drivers/acpi/nfit/intel.c:692:35: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
> > 
> > One sample warning is good.
> > 
> > How about adding a comment on why the usage of __struct_group() here
> > means this doesn't break userspace.
> > 
> > snip
> > 
> > > diff --git a/include/uapi/linux/ndctl.h b/include/uapi/linux/ndctl.h
> > > index 73516e263627..34c11644d5d7 100644
> > > --- a/include/uapi/linux/ndctl.h
> > > +++ b/include/uapi/linux/ndctl.h
> > 
> > FWIW: In a patch like this where reviewers likely want to see
> > the header file change first, put it first in the diff.
> > (git diff.orderfile)
> 
> TIL about diff.orderfile! :) Just for my own education, what do you have
> as the contents for your orderfile? Is it just simply:
> 
> *.h
> 
> ?

I've updated my local environment to use this, to see how well it ends up
behaving:

Kconfig
*/Kconfig
*/Kconfig.*
Makefile
*/Makefile
*/Makefile.*
scripts/*
Documentation/*
*.h
*.S
*.c
tools/testing/*

https://github.com/kees/kernel-tools/commit/909db155b5cd36832d10d7d9932d7b51b46388aa

-Kees

-- 
Kees Cook